Method of upgrading a fischer-tropsch light oil

ABSTRACT

The product of Fischer-Tropsch synthesis is separated to recover a C 5  -400° F liquid fraction which is thereafter upgraded to a higher octane gasoline fraction and a low-pour, high diesel index fuel oil by a &#34;dense phase&#34; process using HZSM-5 and related zeolites as catalysts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is concerned with a process for converting synthesis gas,i.e. mixtures of gaseous carbon oxides with hydrogen or hydrogen donors,to hydrocarbon mixtures and oxygenates. More particularly, thisinvention is concerned with upgrading a C₅ + fraction having an endpoint of 340° up to 400° F. obtained in a known Fischer-Tropschsynthesis process, so as to obtain a high yield of C₅ + gasoline ofenhanced octane and a low-pour, high diesel index fuel oil.

2. Other Prior Art

Processes for the conversion of coal and other hydrocarbons, such asnatural gas to a gaseous mixture consisting essentially of hydrogen andcarbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen andcarbon monoxide and carbon dioxide, are well known. Although variousprocesses may be employed for the gasification, those of majorimportance depend either on the partial combustion of the fuel with anoxygen-containing gas or on a combination of these two reactions. Anexcellent summary of the art of gas manufacture, including synthesisgas, from solid and liquid fuels, is given in "Encyclopedia of ChemicalTechnology", edited by Kirk-Othmer, Second Edition, Volume 10, pages353-433 (1966), Interscience Publishers, New York; the contents of whichare herein incorporated by reference. The techniques for gasification ofcoal or other solid, liquid or gaseous fuel are not considered to be perse inventive here.

It is considered desirable to effectively and more efficiently convertsynthesis gas, and thereby coal and natural gas, to highly valuedhydrocarbons such as motor gasoline with high octane number,petrochemical feedstocks, liquefiable petroleum fuel gas, and aromatichydrocarbons. It is well known that synthesis gas will undergoconversion to form reduction products of carbon monoxides, such ashydrocarbons at from about 300° F. to about 850° F. under from about oneto one thousand atmospheres pressure, over a fairly wide variety ofcatalysts. The Fischer-Tropsch process, for example, which has been mostextensively studied, produces a range of products including liquidhydrocarbons, a portion of which have been used as low octane gasoline.The types of catalysts that have been studied for this and relatedprocesses include those based on metals or oxides of iron, cobalt,nickel, ruthenium, thorium, rhodium and osmium.

The wide range of catalysts and catalysts modifications disclosed in theart and an equally wide range of conversion conditions for the reductionof carbon monoxide by hydrogen provide considerable flexibility towardobtaining selected boiling-range products. Nonetheless, in spite of thisflexibility it has not proved possible to make such selections so as toproduce liquid hydrocarbons in the gasoline boiling range which containhighly branched paraffins and substantial quantities of aromatichydrocarbons, both of which are required for high quality gasoline, orto selectively produce aromatic hydrocarbons particularly rich in thebenzene to xylene range. A review of the status of this art is given in"Carbon Monoxide-Hydrogen Reactions", Encyclopedia of ChemicalTechnology, edited by Kirk-Othmer, Second Edition, Volume 4, pp.446-488, Interscience Publishers, New York, the text of which isincorporated herein by reference.

Recently, a method for upgrading the C₅ + liquid product of aFischer-Tropsch synthesis having an end point from about 340°-400° F.has been discovered, which method comprises pretreating the C₅ + liquidproduct by hydrogenating it in the presence of a hydrogenation component(such as platinum or palladium) at conditions of temperature andpressure so as to selectively hydrogenate the diolefins contained in theC₅ + liquid product and thereafter contacting the hydrogenated product,at a temperature within the range of about 575° to 850° F. and at apressure within the range of about atmospheric to 700 psig, with acrystalline aluminosilicate having certain well-defined characteristics.This method is described in a copending United States patentapplication, Ser. No. 684,511, filed May 7, 1976, now U.S. Pat. No.4,052,477. It should be noted that the elevated temperatures of the stepfollowing pretreatment are such that most or substantially all of thehydrogenated product from the pretreatment step will be in the gaseousphase during the second, aluminosilicate contacting step.

SUMMARY OF THE INVENTION

This invention is concerned with improving the product distribution andyield of products obtained by a Fischer-Tropsch synthesis gas conversionprocess. In a particular aspect, the present invention is concerned withupgrading the C₅ -400° F. liquid fraction of a synthesis gas conversionoperation known in the industry as the Sasol Synthol process.

The Sasol process, located in South Africa, and built to convert anabundant supply of poor quality coal and products thereof toparticularly hydrocarbons, oxygenates and chemical forming componentswas a pioneering venture. The process complex developed is enormous,expensive to operate and may be conveniently divided or separated into(1) a synthesis gas preparation complex from coal, (2) a Fischer-Tropschtype of synthesis gas conversion in both a fixed catalyst bed operationand a fluid catalyst bed operation, (3) a product recovery operation and(4) auxillary plant and utility operations required in such a complex.

The extremely diverse nature of the products obtained in the combinationoperation of the Sasol process amplifies the complexity of the overallprocess complex, its product recovery arrangement and its operatingeconomics. The Sasol synthesis operation is known to produce a widespectrum of products including fuel gas, light olefins, LPG, gasoline,light and heavy fuel oils, waxy oils and oxygenates identified asalcohols, acetone, ketones and acids, particularly acetic and propionicacid. The C₂ and lower boiling components may be reformed to carbonmonoxide and hydrogen or the C₂ formed hydrocarbons and methane may becombined and blended for use in a fuel gas pipeline system.

In the Sasol operation, the water-soluble chemicals are recovered as bysteam stripping distillation and separated into individual componentswith the formed organic acids remaining in the water phase separatelytreated. Propylene and butylene formed in the process are converted togasoline boiling components as by polymerization in the presence of aphosphoric acid catalyst and by alkylation. Propane and butane on theother hand are used for LPG.

The present invention is concerned with improving a Fischer-Tropschsynthesis gas conversion operation and is particularly directed toimproving the synthetic gasoline product selectively and qualityobtained by processing C₅ -400° F. material over a special class ofcrystalline zeolite represented by HZSM-5 crystalline zeolite andrelated catalysts. It has been found that improved benefits can beobtained with regard to such processing if the pressures andtemperatures of the contacting zone are such that most of the charge andproduct components are in the liquid phase, thereby washing off cokeprecursors and minimizing the rate of catalyst aging. A particular andunexpected benefit of the "dense phase" processing as compared to the"gaseous phase" processes is that it yields a by-product, high qualityfuel oil, and at the same time upgrades the C₅ -400° F. material to ahigher octane number. Moreover, the gas make of the method of thepresent invention is less than 1 percent, as compared to the 10-15percent gas formation encountered in the "gaseous phase" processes.

Although combined oxygen in the charge is only partially removed by thepresent invention, complete oxygen removal is possible by a subsequenthydrotreatment of the gasoline product over a Co/Mo/Al catalyst at50-300 p.s.i.g., 500°-600° F., 0.2-10 LHSV, and 200-700 SCF H₂ /bbl,with little or no octane loss. Finally, it is not necessary to pretreatthe C₅ -400° F. charge by hydrogenating the diolefins contained therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a condensed, schematic, block-flow arrangement of a knownFischer-Tropsch syngas conversion process directed to the conversion ofcoal to synthesis gas comprising carbon monoxide and hydrogen and thereduction of carbon monoxide by the Fischer-Tropsch process to form aproduct mixture comprising hydrocarbon and oxygenates and the recoveryof these products for further use.

FIG. 2 is a plot of yields of C₅ -400° F. gasoline, 400°-650° F. fueloil, and 650° F.+ product versus liquid product gravity, which plot isderived from an example of a process incorporating the presentinvention.

FIG. 3 is a yield-octane plot for C₅ -400° F. gasoline produced in anexample of a process incorporating the present invention.

DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown in block flow arrangement asubstantially reduced process flow arrangement of the Sasol syngasconversion process. A coal gasifier section 2 is provided to whichpulverized coal is introduced by conduit 4, steam by conduit 6 andoxygen by conduit 8. The products of gasifier section 2 are then passedby conduit 10 to a gas scrubber section 12. In scrubber section 12,carbon monoxide and hydrogen-producing gases are separated from hydrogensulfide which is removed by conduit 14, carbon dioxide removed byconduit 16, tars and phenols removed by conduit 18 and ammonia removedby conduit 20. The carbon monoxide-hydrogen producing gas is passed fromsection 12 by conduit 22 to a partial combustion zone 24 supplied withsteam by conduit 26 and oxygen by conduit 28. Recycle C₂ fuel gasproduct of the combination process after separation of carbon dioxidetherefrom is recycled by conduit 30 to the partial combustion section24. In the partial combustion operation 24, a suitable carbonmonoxide-hydrogen rich synthesis gas of desired ratio is formed for usein a downstream Fischer-Tropsch synthesis gas conversion operation.

The Sasol process operates two versions of the Fischer-Tropsch process;one being a fixed catalyst bed operation and the other being a fluidcatalyst bed operation. Each of these operations use iron catalystprepared and presented to obtain desired catalyst composition andactivity. The synthesis gas prepared as above briefly identified ispassed by conduit 32 to the Fischer-Tropsch reaction section 36 inadmixture with recycle gas introduced at a temperature of about 160° C.and at an elevated pressure of about 365 psig. The temperature of thesynthesis gas admixed with catalyst in the fluid operation rapidly risesby the heat liberated so that the Fischer-Tropsch and water gas shiftreactions take place. The products of the Fischer-Tropsch synthesisreaction are conveyed by conduit 38 to a primary cooling section 40wherein the temperature of the mixture is reduced to within the range of280° to about 400° F. In a primary cooling section, a separation is madewhich permits the recovery of a slurry oil and catalyst stream byconduit 42, and a decant oil stream by conduit 44. In one typicaloperation, the decant oil stream will have an ASTM 95% boiling point ofabout 900° F. A light oil stream boiling below about 560° F. and lowerboiling components including oxygenates is passed by conduit 46 to asecond or final cooling and separating section 48. In cooling section48, a separation is made to recover a water phase comprisingwater-soluble oxygenates and chemicals withdrawn by conduit 50, arelatively light hydrocarbon phase boiling below about 560° F. withdrawnby conduit 52 and a normally vaporous phase withdrawn by conduit 54. Aportion of the vaporous phase comprising unreacted carbon monoxide andhydrogen is recycled by conduit 34 to conduit 32 charging syngas to theFischer-Tropsch synthesis operation. In a typical operation, about onevolume of fresh feed is used with two volumes of recycle gas. Thehydrocarbons do not completely condense and an absorber system is usedfor their recovery. Methane and C₂ hydrocarbons are blended with othercomponents in a pipeline system or they are passed to a gas reformingsection for recycle as feed gas in the synthesis operation. The lighthydrocarbon phase in conduit 52 is then passed through a water washsection 56 provided with wash water by conduit 58. In wash section 56,water-soluble materials comprising oxygenates are removed and withdrawntherefrom by conduit 60. The water phases in conduits 50 and 60 arecombined and passed to a complicated and expensive-to-run chemicalsrecovery operation 62. The washed light hydrocarbon phase is removed byconduit 64 and passed to a clay treater 66 along with hydrocarbonfraction boiling below about 650° F. recovered from the decanted oilphase in conduit 44 and a heavy oil product fraction recovered ashereinafter described. The hydrocarbon phase thus recovered and passedto this clay treating section is preheated to an elevated temperature ofabove about 600° F. or higher before contacting the catalyst or clay inthe treater. This clay treatment isomerizes hydrocarbons andparticularly the alpha olefins in the product, thereby imparting ahigher octane rating to these materials. The treatment also operates toconvert harmful acids and other oxygenates retained in the hydrocarbonphase after the water wash. The clay treated hydrocarbon product ispassed by conduit 68 to a hydrocarbon separation reaction 70. A portionof the hydrocarbon vapors in conduit 54 not directly recycled to theFischer-Tropsch conversion operation by conduit 34 is also passed to thehydrocarbon separation reaction 70. In the hydrocarbon separationsection 70, a separation is made to recover a fuel gas stream comprisingC₂ hydrocarbons withdrawn by conduit 72. A portion of this material ispassed through a CO₂ scrubber 74 before recycle by conduit 30 to thepartial combustion zone 24. A portion of the fuel gas may be withdrawnby conduit 76. In separation section 70, a C₂ olefin rich stream isrecovered by conduit 78 for chemical processing as desired. A C₃ to C₄hydrocarbon stream rich in olefins is withdrawn by conduit 80 and passedto catalytic polymerization in section 82. Polymerized material suitablefor blending with gasoline product is withdrawn by conduit 84. A C₅ +gasoline product fraction having an end point in the range of 340° to360° up to 400° F. is recovered by conduit 86 and a light fuel oilproduct such as No. 2 fuel oil is withdrawn by conduit 90 for admixturewith the decant oil fraction in conduit 44 as mentioned above. The blendof hydrocarbons product thus formed will boil in the range of about 400°F. to about 1000° F. This material blend is passed to a separatorsection 92 wherein a separation is made to recover a fraction boiling inthe range of from about 400° to 650° F. withdrawn by conduit 44 from aheavier higher boiling waxy oil withdrawn by conduit 96.

In this relatively complicated synthesis gas conversion operation andproduct recovery, it is not unusual to recover a product distributioncomprising 2% ethylene, 8% LPG, 70% gasoline boiling material, 3% fueloil, 3% waxy oil and about 14% of materials defined as oxygenates.

This Fischer-Tropsch synthesis operation above briefly defined and knownin the industry as the Sasol Synthol process can be significantlyimproved following the concepts of this invention. It is the purpose ofthe invention to substantially upgrade the C₅ -340° to 400° F. gasolinefraction (i.e. the product from conduit 86 prior to blending via conduit84) by "dense phase" processing over a special type of crystallinealuminosilicate zeolite catalyst.

The special zeolite catalysts referred to herein utilize members of aspecial class of zeolite exhibiting some unusual properties. Thesezeolites induce profound transformations of aliphatic hydrocarbons toaromatic hydrocarbons in commercially desirable yields and are generallyhighly effective in alkylation, isomerization, disproportionation andother reactions involving aromatic hydrocarbons. Although they haveunusually low alumina contents, i.e. high silica to alumina ratios, theyare very active even with silica to alumina ratios exceeding 30. Thisactivity is surprising since catalytic activity of zeolites is generallyattributed to framework aluminum atoms and cations associated with thesealuminum atoms. These zeolites retain their crystallinity for longperiods in spite of the presence of steam even at high temperatureswhich induce irreversible collapse of the crystal framework of otherzeolites, e.g. of the X and A type. Furthermore, carbonaceous deposits,when formed, may be removed by burning at higher than usual temperaturesto restore activity. In many environments, the zeolites of this classexhibit very low coke forming capability conducive to very long times onstream between burning regenerations.

An important characteristic of the crystal structure of this class ofzeolites is that it provides constrained access to and egress from theintra-crystalline free space by virtue of having a pore dimensiongreater than about 5 Angstroms and pore windows of about a size such aswould be provided by 10-membered rings of oxygen atoms. It is to beunderstood, of course, that these rings are those formed by the regulardisposition of the tetrahedra making up the anionic framework of thecrystalline aluminosilicate, the oxygen atoms themselves being bonded tothe silicon or aluminum atoms at the centers of the tetrahedra. Briefly,the preferred zeolites useful as catalysts in this invention possess, incombination: a silica to alumina ratio of at least about 12; and astructure providing constrained access to the crystalline free space.

The silica to alumina ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminaratio of at least 12 are useful, it is preferred to use zeolites havinghigher ratios of at least about 30. Such zeolites, after activation,acquire an intra-crystalline sorption capacity for normal hexane whichis greater than that for water, i.e. they exhibit "hydrophobic"properties. It is believed that this hydrophobic character isadvantageous in the present invention.

The zeolites useful as catalysts in this invention freely sorb normalhexane and have a pore dimension greater than about 5 Angstroms. Inaddition, their structure must provide constrained access to some largermolecules. It is sometimes possible to judge from a known crystalstructure whether such constrained access exists. For example, if theonly pore windows in a crystal are formed by 8-membered rings of oxygenatoms, then access by molecules of larger cross-section than normalhexane is substantially excluded and the zeolite is not of the desiredtype. Zeolites with windows of 10-membered rings are preferred, althoughexcessive puckering or pore blockage may render these zeolitessubstantially ineffective. Zeolites with windows of 12-membered rings donot generally appear to offer sufficient constraint to produce theadvantageous conversions desired in the instant invention, althoughstructures can be conceived, due to pore blockage or other cause, thatmay be operative.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access, a simpledetermination of the "constraint index" may be made by continuouslypassing a mixture of equal weight of normal hexane and 3-methylpentaneover a small sample, approximately 1 gram or less, of zeolite atatmospheric pressure according to the following procedure. A sample ofthe zeolite, in the form of pellets or extrudate, is crushed to aparticle size about that of coarse sand and mounted in a glass tube.Prior to testing, the zeolite is treated with a stream of air at 1000°F. for at least 15 minutes. The zeolite is then flushed with helium andthe temperature adjusted between 550° F. and 950° F. to give an overallconversion between 10% and 60%. The mixture of hydrocarbons is passed at1 liquid hourly space velocity (i.e. 1 volume of liquid hydrocarbon pervolume of catalyst per hour) over the zeolite with a helium dilution togive a helium to total hydrocarbon mole ratio of 4:1. After 20 minuteson stream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromatography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

The constraint index is calculated as follows: ##EQU1##

The constraint index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Catalysts suitable for the presentinvention are those which employ a zeolite having a constraint indexfrom 1.0 to 12.0. Constraint Index (CI) values for some typicalzeolites, including some not within the scope of this invention are:

    ______________________________________                                        CAS                      C.I.                                                 ______________________________________                                        ZSM-5                    8.3                                                  ZSM-11                   8.7                                                  ZSM-35                   4.5                                                  TMA Offretite            3.7                                                  ZSM-12                   2                                                    ZSM-38                   2                                                    Beta                     0.6                                                  ZSM-4                    0.5                                                  Acid Mordenite           0.5                                                  REY                      0.4                                                  Amorphous Silica-alumina 0.6                                                  Erionite                 38                                                   ______________________________________                                    

The above-described Constraint Index is an important and even criticaldefinition of those zeolites which are useful to catalyze the instantprocess. The very nature of this parameter and the recited technique bywhich it is determined, however, admit of the possibility that a givenzeolite can be tested under somewhat different conditions and therebyhave different constraint indexes. Constraint Index seems to varysomewhat with severity of operation (conversion). Therefore, it will beappreciated that it may be possible to so select test conditions toestablish multiple constraint indexes for a particular given zeolitewhich may be both inside and outside the above-defined range of 1 to 12.

Thus, it should be understood that the "Constraint Index" value as usedherein is an inclusive rather than an exclusive value. That is, azeolite when tested by any combination of conditions within the testingdefinition set forth hereinabove to have a constraint index of 1 to 12is intended to be included in the instant catalyst definition regardlessthat the same identical zeolite tested under other defined conditionsmay give a constraint index value outside of 1 to 12.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11,ZSM-12, ZSM-21, ZSM-35, ZSM-38 and other similar material. Recentlyissued U.S. Pat. No. 3,702,886 describing and claiming ZSM-5 isincorporated herein by reference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 832,449, theentire contents of which are incorporated herein by reference.

U.S. application Ser. No. 358,192, filed May 7, 1973, now U.S. Pat. No.4,016,245 the entire content of which are incorporated herein byreference, describes a zeolite composition and a method of making such,designated as ZSM-21 which is useful in this invention.

U.S. application Ser. No. 528,061, filed Nov. 29, 1974, the entirecontents of which are incorporated herein by reference, describes azeolite composition including a method of making it. This composition isdesignated ZSM-35 and is useful in this invention.

U.S. application Ser. No. 528,060, filed Nov. 29, 1974 and nowabandoned, the entire contents of which are incorporated herein byreference, describes a zeolite composition including a method of makingit. This composition is designated ZSM-38 and is useful in thisinvention.

The X-ray diffraction pattern of ZSM-21 appears to be generic to that ofZSM-35 and ZSM-38. Either or all of these zeolites is considered to bewithin the scope of this invention.

The specific zeolites described, when prepared in the presence oforganic cations, are substantially catalytically inactive, possiblybecause the intracrystalline free space is occupied by organic cationsfrom the forming solution. They may be activated by heating in an inertatmosphere at 1000° F. for one hour, for example, followed by baseexchange with ammonium salts followed by calcination at 1000° F. in air.The presence of organic cations in the forming solution may not beabsolutely essential to the formation of this special type zeolite;however, the presence of these cations does appear to favor theformation of this special type of zeolite. More generally, it isdesirable to activate this type zeolite by base exchange with ammoniumsalts followed by calcination in air at about 1000° F. for from about 15minutes to about 24 hours.

Natural zeolites may sometimes by converted to this type zeolite byvarious activation procedures and other treatments such as baseexchange, steaming, alumina extraction and calcination, alone or incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulanditeand clinoptilolite. The preferred crystalline aluminosilicates areZSM-5, ZSM-11, ZSM-12 and ZSM-21, with ZSM-5 particularly preferred.

The zeolites used as catalysts in this invention should be essentiallyin the hydrogen form. They may be base exchanged or impregnated tocontain a Group VIII metal for enhanced stability. It is desirable tocalcine the zeolite after base exchange. The metal cations that may bepresent include any of the cations of the metals of Group VIII of theperiodic table.

In a preferred aspect of this invention, the zeolites useful ascatalysts herein are selected as those having a crystal frameworkdensity, in the dry hydrogen form, of not substantially below about 1.6grams per cubic centimeter. It has been found that zeolites whichsatisfy all three of these criteria are most desired. Therefore, thepreferred catalysts of this invention are those comprising zeoliteshaving a constraint index as defined above of about 1 to 12, a silica toalumina ratio of at least about 12 and a dried crystal density of notsubstantially less than about 1.6 grams per cubic centimeter. The drydensity for known structures may be calculated from the number ofsilicon plus aluminum atoms per 1000 cubic Angstroms, as given, e.g. onpage 19 of the article on Zeolite Structure by W. M. Meier. This paper,the entire contents of which are incorporated herein by reference, isincluded in "Proceedings of the Conference on Molecular Sieves, London,April 1967" published by the Society of Chemical Industry, London, 1968.When the crystal structure is unknown, the crystal framework density maybe determined by classical pyknometer techniques. For example, it may bedetermined by immersing the dry hydrogen form of the zeolite in anorganic solvent which is not sorbed by the crystal. It is possible thatthe unusual sustained activity and stability of this class of zeolitesis associated with its high crystal anionic framework density of notless than about 1.6 grams per cubic centimeter. This high density, ofcourse, must be associated with a relatively small amount of free spacewithin the crystal, which might be expected to result in more stablestructures. This free space, however, seems to be important as the locusof catalytic activity.

Crystal framework densities of some typical zeolites including somewhich are not within the purview of this invention are:

    ______________________________________                                                  Void               Framework                                        Zeolite   Volume             Density                                          ______________________________________                                        Ferrierite                                                                              0.28      cc/cc    1.76     g/cc                                    Mordenite .28                1.7                                              ZSM-5, -11                                                                              .29                1.79                                             Dachiardite                                                                             .32                1.72                                             L         .32                1.61                                             Clinoptilolite                                                                          .34                1.7                                              Laumontite                                                                              .34                1.77                                             ZSM-4 (Omega)                                                                           .38                1.65                                             Heulandite                                                                              .39                1.69                                             P         .41                1.57                                             Offretite .40                1.55                                             Levynite  .40                1.54                                             Erionite  .35                1.51                                             Gmelinite .44                1.46                                             Chabazite .47                1.45                                             A         .5                 1.3                                              Y         .48                1.27                                             ______________________________________                                    

As has heretofore been stated, the most preferred form of the specific,previously defined zeolites in carrying out the novel process of thisinvention is the hydrogen form. As acid form is well known in the art,the hydrogen form can be made by base exchanging the particular zeolitewith hydrogen ions or ions capable of conversion to hydrogen ions, i.e.ammonium ions.

The crystalline zeolite compositions can also be admixed with anon-acidic inorganic binder, such as alumina in order to impart thedesired properties to the zeolite, such as increased strength andattrition resistance. Quite obviously, the proportion of binder employedis not narrowly critical, and it has been found convenient to usecompositions where the binder is present from about 10 to 70% andpreferably 30-40% based on the total weight of the zeolite plus binder.

By the term "dense phase" processing, as used herein, is meant themaintenance of most of the charge and product in contact with thecatalyst of this invention is the liquid phase. The quantity of chargeand product present in the liquid phase is preferably greater than 90percent of the total quantity of charge and product in contact with thecatalyst. The operating conditions of the dense phase technique arepressures of 200 to 1000 psig, no hydrogen, temperatures of the order of400° to 700° F. and LHSV of 0.1 to 2. As was mentioned previously, theprimary purpose of the technique is to minimize catalyst aging byallowing the liquid phase charge and product to "wash off" cokeprecursors from the catalyst surface. Preferred operating conditions arepressures of 600 to 700 psig, no hydrogen, temperatures of 450° to 560°F. and LHSV of 0.1 to 1.0.

Since a pure gas at temperature above its critical temperature cannot beliquefied, regardless the degree of compression, it is essential thatthe temperature of process of this invention be well below the criticalpoint of the mix present in the catalyst contacting zone. The criticalpoint of the mix represents the condition at which the specificproperties of the liquid and gas phases become identical, causing thephases to be indistinguishable. To indicate the range of the criticalproperties of the substances contained in C₅ -400° F. charge and theproducts of the process of this invention, the following properties ofvarious hydrocarbons have been selected from F. P. Rossini et al.,"Selected Values of Physical and Thermodynamic Properties ofHydrocarbons and Related Compounds", Carnegie Press, Pittsburgh,Pennsylvania, 1953:

    ______________________________________                                        Pentene-1       394° F                                                                             586 psi                                           n-Pentane       386° F                                                                             490 psi                                           n-Hexane        455° F                                                                             440 psi                                           n-Heptane       512° F                                                                             397 psi                                           n-Octane        565° F                                                                             362 psi                                           n-Nonane        611° F                                                                             331 psi                                           n-Decane        654° FG                                                                            306 psi                                           ______________________________________                                    

Critical properties for olefins greater than C₅ were not included byRossini but may be estimated by methods such as the one described byGambill in Chemical Engineering, June 15, 1959, pp. 182-83; and ChemicalEngineering, July 13, 1959, pp. 157-160; or by Nokay in ChemicalEngineering, Feb. 23, 1959, p. 146.

The following example illustrates the best mode now contemplated forcarrying out this invention.

EXAMPLE I

A C₅ -400° F. liquid fraction product of Fischer-Tropsch synthesis waspassed over HZSM-5 extrudate at 700 psig, 0.6-1 LHSV, and temperaturesof 450°-560° F. for a period of 21 days. Properties of the C₅ -400° F.charge are shown in Table I. The HZSM-5 extrudate contained 35 percentalumina binder, was sized to 30-60 mesh, and was charged to a 9/32inches i.d. S.S. tubing reactor where it was pretreated with hydrogen at900° F. for one hour. After catalyst pretreatment, the reactor waspressured to 700 psig with nitrogen against a groove loader, and thenthe C₅ -400° F. charge pumped down-flow over the catalyst bed atreaction temperature. The run was started at 450° F., under whichcondition all components except the C₅ 's were liquid. At 560° F. theC₈ + components remain in the liquid phase, but at temperatures above560° F. aging rates would be expected to accelerate because of the lossof the "dense phase" condition characteristic of this invention.Analysis of the C₅ components concentrated in the liquid product wasaccomplished by the gas chromatographic technique, and the liquidproduct was fractionated in Vigereaux column with cut points at 400° and650° F. Results of the Example are summarized in Table I:

                                      TABLE I                                     __________________________________________________________________________    Time on Stream, Days                                                                           Charge                                                                            7   8   14  21                                           __________________________________________________________________________    Process Conditions                                                            LHSV             --  0.60                                                                              0.62                                                                              0.62                                                                              0.58                                         Average Temp., ° F                                                                      --  506 453 506 505                                          Properties of Total Liquid Product                                            Gravity, ° API                                                                          58.9                                                                              48.8                                                                              54.3                                                                              52.1                                                                              55.1                                         Oxygen, wt. %    1.6 0.7 0.7 --  --                                           Yields, wt. % of Oil Charge                                                   C.sub.1 -C.sub.4 0.1 1.5 0.6 0.2 0.3                                          C.sub.5, total   4.1 2.5 2.8 2.2 3.4                                          C.sub.5, olefinic                                                                              3.5 0.9 1.0 1.4 2.8                                          C.sub.6 +        95.8                                                                              96.0                                                                              96.6                                                                              97.6                                                                              96.3                                         C.sub.6 Olefin Distribution, wt. %                                            of Total C.sub.5 Olefinic Yield                                               1-Pentene        75  <1  <1  2   6                                            2-Methyl-1-butene                                                                              9   17  17  15  7                                            3-Methyl-1-butene                                                                              6   <1  <1  1   1                                            trans-2-Pentene  4   10  10  16  42                                           cis-2-Pentene    4   4   5   7   19                                           2-Methyl-2-butene                                                                              2   69  68  59  25                                           Properties of Liquid                                                          Product Fractions                                                             C.sub.5 -400° F Gasoline                                               wt.% of charge   100 55.2                                                                              79.1                                                                              71.0                                                                              82.7                                         Gravity, °  API                                                                         66.0                                                                              85.9                                                                              83.3                                                                              84.7                                                                              82.3                                         Octane No. (R+O) 66.0                                                                              85.9                                                                              83.3                                                                              84.7                                                                              82.3                                         Oxygen, wt. %    1.6 0.8 0.8 0.9 0.9                                          400-650° F Fuel Oil                                                    wt. % of Charge  --  35.2                                                                              20.3                                                                              26.1                                                                              17.0                                         Gravity, ° API                                                                          --  42.6                                                                              38.0                                                                              42.0                                                                              36.3                                         Pour Point, ° F                                                                         --  <-70                                                                              <-65                                                                              <-70                                                                              <-70                                         Aniline No. ° F                                                                         --  147.8                                                                             131.5                                                                             142.0                                                                             124.0                                        Diesel Index     --  63.0                                                                              50.0                                                                              59.6                                                                              45.4                                         650° F + Product                                                       wt. % of Charge  --  8.1 --  2.7 --                                           __________________________________________________________________________

Gravity of the total (i.e. unfractionated) liquid product was used tomonitor conversion of the C₅ -400° F. liquid fraction from theFischer-Tropsch synthesis to higher boiling products and also to monitorcatalyst aging. FIG. II is a plot of yields of C₅ -400° F. gasoline,400° F.-650° F. fuel oil, and 650° F. product versus total liquidproduct gravity, °API.

Another indicator of catalyst activity in the process of this inventionis the C₅ olefin composition. For example, an examination of the dataincluded in Table I indicates an increase in the 1-Pentene content and acorresponding decrease in the 2-Methyl-2-butene content of the productC₅ olefins after 21 days on stream. From this information, some catalystaging may be inferred. However, a pump failure occurred early in the runresulting in an approximately 25 hour soak at 550° F., which would beexpected to deposit coke on the catalyst. Nevertheless, considering thefact that the catalyst was functioning well at 500° F. after 14 days ofoperation despite the experimental shortcomings, it is both reasonableand justifiable to expect that the dense phase process of this inventionwill effect at least a 1-month catalyst cycle at the 70%+ gasoline yieldlevel.

The yield-octane plot for C₅ -400° F. gasoline product, shown in FIG.III, shows a 12 volume percent yield loss to 400°-650° F. fuel oilproduct for the first 15 octane number increase (i.e. from 66 to 81R.O.N.). Little further increase beyond 85 R.O.N. (R+O) is expectedregardless of further gasoline loss and this expectation is supported byFIG. III. This relationship is predictable because of the existence ofresidual, low-octane paraffins, which are not reacted. Rapidisomerization of the 1-olefins, along with polymerization to the400°-650° F. fuel oil product accounts for the rapid initial octanegain. However, further octane gain requires disappearance of theslower-polymerizing, internal and branched olefins plus furtherisomerization. Finally, the following mass spectrographic P/O/N/Aanalyses of the C₄ -400° F. gasoline products (see Table II) show thataromatic content increases with octane number, but this increase can beaccounted for primarily by the concentration of the original aromaticsin the feed -- not the formation of additional aromatic compounds.

                  TABLE II                                                        ______________________________________                                         P/O/N/A Analyses of Gasoline Products                                        ______________________________________                                        Gasoline Yield, wt. %                                                                          100     79     71    55                                      Days on Stream (See Table I)                                                                   Charge   8     14     7                                      Paraffins, Vol. %                                                                               9      10     15    18                                      Olefins, Vol. %  --      82     68    56                                      Naphthenes, Vol. %                                                                             --       1      2     3                                      Aromatics, Vol. %                                                                              --       7     15    23                                      Octane No. (R+O)  66     83.3   84.7  85.9                                    ______________________________________                                    

The properties of the 400°-650° F. fuel oil product are shown below inTable III as a function of the severity of dense phase processing.

                  TABLE III                                                       ______________________________________                                        400-650° F Product Yield                                                                   20      26      35                                        Days on Stream (see Table I)                                                                      8       14      7                                         Gravity, ° API                                                                             38.8    42.0    42.6                                      Boiling Range, ° F (Simulated                                          Distillation, ASTM Method D-2887)                                             10%                 --      421     422                                       50%                 --      510     497                                       90%                 --      613     600                                       98%                 --      661     637                                       Pour Point, ° F                                                                            <-65    <-70    <-70                                      Aniline No., ° F                                                                           131.5   142.0   147.8                                     Diesel Index        50      60      63                                        ______________________________________                                    

The data in Table III, particularly the low pour points coupled with thehigh aniline numbers, indicate that the 400°-650° F. product is ahighly-branched, non-aromatic fuel. Furthermore, when the total 400° F.+product after 7 days on stream was collected, it was found to have apour point of -75° F., an aniline number of 152.5, a gravity of 40.5°API, and a diesel index of 62. Thus, the 650° F.+ product may beincluded in the 400° F. product and the resulting 400° F.+ fraction usedas a No. 2 fuel oil. However, the 650° F.+ product by itself is probablyof limited commerical importance because of its low viscosity index (the650° F.+ fraction after 7 days on stream had a pour point of -20° F., akinetic viscosity at 100° F. of 26.64 cs, a kinetic viscosity at 210° F.of 4.50 cs., and a viscosity index of 82).

What is claimed is:
 1. In a method for upgrading a product ofFischer-Torpsch synthesis boiling within the range of C₅ to 400° F. togasoline and fuel oil product by contacting a crystallinealuminosilicate catalyst characterized by a pore dimension greater than5 Angstroms, a silica to alumina ratio of at least 12 and a constraintindex within the range of 1 to 12, the improvement which comprises,(a)effecting contact of said Fischer-Tropsch synthesis product boilingwithin the range of C₅ to 400° F. maintained at least 90 percent inliquid phase with said crystalline aluminosilicate catalyst in theabsence of hydrogen at a pressure within the range of 200 to 1000 psig,maintaining the temperature during said contact within the range of 400°to 560° F. and a liquid hourly space velocity within the range of 0.1 to2, and (b) recovering a C₅ plus gasoline product of improved octane anda fuel oil product from said liquid phase upgrading operation.
 2. Themethod of claim 1 wherein the temperature is at least 450° F. and thespace velocity is below 1.0.
 3. The method of claim 1 wherein thecrystalline aluminosilicate is exchanged with one of hydrogen ions orammonium ions.
 4. The method of claim 1 wherein the crystallinealuminosilicate is selected from the group consisting of ZSM-5, ZSM-11,ZSM-12, ZSM-35 and ZSM-38.
 5. The method of claim 1 wherein the gasolineproduct is hydrotreated in the presence of a cobalt-molybdenum-aluminacatalyst to produce a deoxygenated gasoline product.
 6. The method ofclaim 1 wherein the zeolite is ZSM-5 and is composited with an inorganicoxide binder.